Generally, background of the invention is presented in the above-mentioned patent(s) and applications. According to the invention a color output is produced using liquid crystal material.
Prior devices using liquid crystal have achieved color output capability. One such device uses twisted nematic liquid crystal material and pleochroic dye to control color filtering of light; such device has been used in a relatively small, e.g. hand held, television display device.
Polarizers are needed for operation of twisted nematic liquid crystal displays, though, and this need is disadvantageous. For example, a polarizer will reduce the amount of transmitted light and, therefore, the overall brightness of the display using the same. The intensity of white output light produced by a twisted nematic liquid crystal display, relying on additive red, green and blue picture elements (analagous to color dots of a color television), will be no greater than about one sixth the intensity of the incident light. The brightness of color light output by the twisted nematic liquid crystal color display also is appreciably smaller than the intensity of the incident light due to the light blocking of a polarizer. Another disadvantage of polarizers in liquid crystal color displays is the color shift that can be caused by a polarizer which will affect the accuracy of the produced color output.
As is described in further detail below, the present invention uses the principles of the nematic curvilinear aligned phase (NCAP) liquid crystal material, which is described in the above-referenced U.S. Patents. Although such NCAP liquid crystalmaterial preferably is of the operationally nematic type, it will be appreciated that other types of liquid crystal material, such as smectic and/or combinations of two or more of the several types of liquid crystal material may be used in the context of the invention as long as such liquid crystal material generally follows the described operationally guidelines to achieve controlled light filtering or coloring in response to a prescribed input.
Such NCAP liquid crystal material is, for example, the combination of operationally nematic liquid crystal material and a surface means that distorts the natural structure of the liquid crystal in the absence of a prescribed input to cause the scattering of light or when pleochroic dye is contained in the liquid crystal material to cause absorption of light. The amount of such scattering or absorption is reduced when a prescribed input, such as an electric field or a magnetic field, is applied to the NCAP liquid crystal material. The color of light absorbed or the color transmitted is a function of the particular color of the pleochroic dye contained in the liquid crystal.
According to a preferred form of the invention, the liquid crystal material is in volumes formed in a containment medium. Such liquid crystal contained in volumes is the preferred NCAP liquid crystal material. The interior wall(s) of the containment medium volumes tend to distort the natural structure of the liquid crystal material to achieve the desired scattering or absorption.
As is well known, there are three main types of liquid crystal material, which include nematic, cholesteric, and smectic.
The present invention preferably uses operationally nematic liquid crystal. One definition of operationally nematic is the liquid crystal is nematic liquid crystal or operates like nematic liquid crystal. Another definition of operationally nematic liquid crystal is a liquid crystal characterized such that in the absence of external fields structural distortion of the liquid crystal is dominated by the orientation of the liquid crystal at its boundaries rather than by bulk effects, such as very strong twists, as in cholesteric material, or layering, as in smectic material. The operationally nematic material may include a mixture of nematic and cholesteric materials; for example, operationally nematic liquid crystal with chiral ingredients, which induce a tendency to twist but cannot overcome the effects of boundary alignment, still would be operationally nematic. Also, for example, a type of smectic material that fits the operational criteria specified may be considered as operationally nematic. Use of operationally nematic liquid crystal enables operational response as a function of electrical input and also enables relatively expeditious and efficient operation, for example in response to the application or removal of an electric field.
Although the present invention preferably employs operationally nematic liquid crystal material, it will be appreciated that the invention may be used with other types of liquid crystal materials than those of the operationally nematic type if such materials function satisfactorily to achieve the described operation of the invention set forth in further detail below. Throughout the following description, though, for convenience, the liquid crystal of the invention may be referred to as nematic or operationally nematic.
Generally a volume of liquid crystal means a quantity of liquid crystal material in a containment medium. The volume of liquid crystal may be a discrete volume, such as a generally curved or, more specifically, spherical, capsule or capsule-like volume bounded on the outside by the containment medium and containing the liquid crystal material within the interior space of the volume. The volume of liquid crystal may be a shape other than spherical. The shape of the interior space (in which the liquid crystal is contained or is confined) within the containment medium may be the same or different shape relative to the shape of the exterior of the containment medium. The volume of liquid crystal may be connected to one or more other volumes of liquid crystal, for example by interconnecting passageways between the interior liquid crystal portions of plural volumes of liquid crystal, by connections of the walls of the containment medium of respective volumes of liquid crystal, or by both. The terms volume, capsule, cell, etc. may be used interchangeably and equivalently herein.
The volume of liquid crystal may be or may be formed or derived from an emulsion, matrix, dispersion, or the like of liquid crystal material and a containment medium or of liquid crystal material in a containment medium. The volume of liquid crystal may be a cell or a cell-like area within a containment medium.
A wall or surface of the containment medium that interfaces with the liquid crystal material is intended to cooperate with the liquid crystal material to distort the liquid crystal structure to a curvilinear alignment form in the absence of a prescribed input, such as an electric field. Such distorted or curvilinear alignment will cause the volume of liquid crystal as well as the pleochroic dye therewith to have a particular optical response or effect on light incident thereon; and in response to a prescribed input, such response can be altered or controlled. Specifically, in the absence of a prescribed input, the distorted curvilinearly aligned liquid crystal material and pleochroic dye contained therein will have a maximum light absorbing or color filtering effect; and in response to such prescribed input (such as an electric field with or without certain frequency characteristics) the amount of such light absorbing or color filtering can be reduced. Also, the prescribed input may include a frequency characteristic to which the liquid crystal may respond to alter or not the alignment characteristics and, thus, the color filtering characteristics.
The prescribed input to which the liquid crystal material of the invention may respond preferably is an electric field; and such response generally is described in detail in the above-referenced patents and/or applications. The electric field may be derived by applying a voltage across a pair of electrodes on opposite sides of the liquid crystal material. The electric field may be alternating current type or direct current type, although the former is preferred. The liquid crystal material is responsive to the magnitude of such electric field to overcome the distortion caused by the surface of the containment medium, and, thus, to align with repsect to the field, generally in proportion to the magnitude of the field. Moreover, the liquid crystal material may be frequency responsive, and in such case the liquid crystal alignment may be a function of both the magnitude and frequency of the applied field. Furthermore, although preferably the prescribed input is an electric field (and will be referred to below interchangeably as prescribed input and electric field), it will be appreciated that the prescribed input may be a magnetic field or other input that is capable of causing the desired operational response according to the invention.
Usually liquid crystal material is anisotropic. One example is optical anisotropy, which is the characteristic of birefringence. A birefringent liquid crystal may have one index of refraction characteristic (ordinary index of refraction) when looking along the axis of the liquid crystal and a different index of refraction characteristic (extraordinary index of refraction) when looking across the axis of the liquid crystal. Another example is electrical anisotropy; liquid crystal, especially nematic liquid crystal, may have positive or negative dielectric anisotropy. Moreover, some liquid crystal materials are referred to as cross over liquid crystal because they may have both positive and negative dielectric anisotropy; and the particular polarity thereof is a function of the frequency of applied electric field. As is described further below, the preferred liquid crystal material of the invention has positive dielectric anisotropy or is of the cross over type.
Pleochroic dye has been used in the past in a mixture with operationally nematic liquid crystal material contained in plural volumes in a containment medium or support medium. The structure of the liquid crystal in the absence of a prescribed input is the distorted alignment referred to herein, which is a result of the influence of the containment medium wall. The pleochroic dye structure tends to follow the structure of the liquid crystal, and, therefore, when so distorted or generally curvilinearly aligned effects substantially a maximum amount of color filtering or light absorption. However, as the liquid crystal tends to align with respect to the prescribed input, e.g. so that the axis of the liquid crystal structure tends to align in parallel with the viewing direction or direction of light transmission through the liquid crystal, the structure of the dye also tends similarly to align causing a reduction in the amount of color filtering or light absorption.
The mentioned alignment of liquid crystal structure and pleochroic dye is generally parallel to the direction of the applied electric field when the liquid crystal has positive dielectric anisotropy; in this aligned condition the dye will have minimal absorption, assuming light transmission also generally in the direction of the field. However, if the liquid crystal has negative dielectric anisotropy, e.g. the liquid crystal being cross over material and the frequency of electric field being above the cross over frequency, the liquid crystal structure and the pleochroic dye will align generally perpendicularly or normal to the direction of the applied field; and if the direction of light transmission still is parallel to the direction of the field, the dye will effect substantially maximum absorption of light (of a particular or of multiple colors).
In one preferred embodiment of the invention the containment medium is polyvinyl alcohol. In another, the containment medium is formed of a latex or latex type material. Epoxy material is another example of a containment medium that may be used. Other containment media that cause operation generally along the lines described in further detail herein also may be used.
In the past, displays using liquid crystal material have had to be relatively small in size for a variety of reasons. Using applicant's invention of providing plural volumes of liquid crystal material in a support or containment medium, relatively large- and small-size displays can be made and operated successfully.
A flat screen television system in which an electroluminescent array is repetitively scanned is disclosed in U.S. Pat. No. 3,627,924. Moreover, U.S. Pat. Nos. 3,636,244 and 3,639,685 disclose signal processing circuits for color television picture tubes. In particular, the latter two patents directly relate to color television signal decoding and utilization in a color television system, and the first-mentioned patent discloses a system for scanning electro-luminescent points in an overall electroluminescent array. Such scanning may be employed in accordance with the present invention, and such signal usage and decoding may be employed, too, according to the present invention to achieve the desired multicolored display output from the liquid crystal color display. The circuits of such disclosures may be used in whole or in part in connection with the present invention to obtain various signals required to achieve desired response from the liquid crystal display of the present invention. The disclosures of such patents hereby are incorporated by reference.
Some exemplary definitions are presented below. These are exemplary only and are not necessarily intended to limit the scope of the invention. The context of the description of the invention will present to those having ordinary skill in the art understanding of various broader and more specific definitions of the elements of the invention and of the equivalents thereof.
Reference to light, light output or input, optical output or input, and similar terms generally means that form of electromagnetic energy or electromagnetic radiation which is in the visible specrum, preferably also including ultraviolet and infrared.
Color generally means the colors of the visible spectrum, preferably also including ultraviolet and infrared. Moreover, depending on the context, geneally reference to color below also includes black and white. Complementary colors generally means two colors that are capable of being mixed to produce, when of substantial purity and equal intensity, a black output. In the context of the present invention a black output means that no light is transmitted. Moreover, in the context of the invention preferably the complementary colors are mixed or are combined optically.
In the context of the present invention, a given color or colored light is derived by the filtering of light incident on a color filtering device. Such color filtering device may be of the band pass or band rejection type, as is described in further detail below. A band pass filter transmits a given color, for example. A band rejection filter prevents the transmission of a particular color or colors. Moreover, the mixing or combining of colors according to the invention preferably is achieved by passing light through multiple color filtering devices.
Examples of complementary colors are green and magenta (magenta sometimes is referred to as a negative green); blue and yellow (yellow sometimes is referred to as a negative blue); and red and cyan (cyan sometimes is referred to as a negative red). A negative color, such as negative green, means that when such negative color is combined optically with the positive color, say green, the result is black; specifically the negative green and the green combine to filter all light and eliminate any transmission. For example, a green band rejection filter would transmit only green light and would block all other colors, and a negative green band rejection filter would block green light and would transmit other colors. Thus, an optical serial arrangement of a green band pass filter and a negative green (actually, magenta, which is a negative green), i.e. a green band rejection, filter would block transmission of incident light so as to produce a black output.
A display is a device which provides an output of the optical type capable of being perceived, discerned, and/or understood. Such optical output preferably is capable of being perceived, discerned and/or understood by a living thing, such as a person or animal, e.g. by visually viewing the optical output. However, such optical output may be perceived, discerned, and/or understood by apparatus, such as automated equipment, optical scanners or readers, etc. Exemplary types of optical outputs include an image, an impression, and information.
An image may be a picture, view, or representation of a scene, of an article, of a person or animal, of something abstract, etc. Such images may be still or moving. An impression may be a collection of colors, or of tones and/or shades of colors, and/or omissions of colors or of tones or shades of colors at selected areas of the display, to present a no color, black, white, single color, multicolor, color gradient, etc. output. For example, such an impression may be a viewable field of blue, black, white, etc. Information may be alpha-numeric characters, symbols, color(s), and/or color sequences that can be viewed, read, comprehended, and/or otherwise capable of causing a response. One form of information may be read and understood by a person; the same or other forms of information may be read by apparatus, such as an optical scanner or reader, etc. The invention can produce images, impressions, information, etc.
A light shutter or optical shutter which has a primary function of controlling light throughput also may be considered a display, especially if the light throughput presents an image, impression and/or information.
The primary thrust of the invention is to displays, preferably of the liquid crystal type, capable of providing a multicolor output (image, impression, information, etc.) capable of being viewed by a person. However, it will be appreciated that the features of the invention may be embodied in other types of displays and the like.